1. Field of the Invention
The invention relates to segments for commutators and more particularly refers to new and improved segments which have a base part of copper or copper alloy and a running layer of carbon which is bonded material-wise to the base part, methods for manufacture of the segments, and the use of such segments.
2. Description of the Prior Art
It is known to improve the commutation of d-c and universal motors through the use of commutators which consist entirely of carbon, or the surface of which is provided with a layer of carbon. The advantage, which is considerable over commutators of metal, is accompanied by some important disadvantages which have so far prevented a larger use of these commutators, particularly,
1. the technically difficult and expensive connection of the winding ends of the commutator winding to the carbon of the segment, PA1 2. the relatively low strength with respect to carbon and its bond with the base, and PA1 3. the high electric resistivity of the carbon relative to copper. PA1 (a) placing a first layer of copper powder and on top thereof a second layer of a mixture of carbon powder and a binder into a die with a cavity shaped like the segment, PA1 (b) densifying the powder layers to produce a blank having the form of the segment, and PA1 (c) sintering the blank at an elevated temperature to cause the powder particles to cohere and the layers to firmly join together.
In composite segments, the higher electric resistivity of the carbon has a smaller effect, with a thinner carbon running layer connected to the metal base. Composite forms also are not subject to the limitations given by the lower strength of the carbon, and there has therefore been no lack of attempts to solve the indicated problems in this manner. For instance, it is known from German Pat. No. 63,622 to apply a thin carbon coating to segments of copper. However, it has not been possible so far to realize on a technical scale the advantages of composite segments which have a metallic base or base part and a running layer consisting essentially of carbon because the strength of the bond between the base part and the running layer was not sufficient. Also the high voltage drop was not satisfactory.